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Data from: Hypoxia drives invertebrate assemblages in agriculturally influenced estuaries

Knysh, Kyle12; Waddell, Jerrica1; Grove, Carissa1; Courtenay, Simon3; van den Heuvel, Michael1

Published Sep 28, 2026 on Dryad. https://doi.org/10.5061/dryad.sn02v6xkk

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Abstract

Estuarine stressors originate from the river-ocean transition and anthropogenic inputs. Agricultural nitrate exports promote macroalgae growth in estuaries, ultimately leading to the production of low-oxygen conditions. Herein examined the extent water-column hypoxia, combined with other environmental factors, influences epibenthic invertebrate assemblages in Prince Edward Island, Canada. First, mobile invertebrate abundances in upper, mid, and lower sites of three eutrophic estuaries were compared to environmental variables. In the following year, invertebrate collections from ten mid-estuary sites were correlated to habitat and stressor variables. Field-sediment toxicity was assessed by amphipod survival through laboratory exposures. Processes along the river-ocean transition impacted invertebrates as abundances of strict-marine taxa declined upstream. In both investigations, tidal variability and associated hypoxia intensity were the predominant factors corresponding with euryhaline taxon abundances. Agricultural intensity did not correspond to Gammarus survival in microcosms. Higher normoxia duration positively correlated with increasing sand-shrimp and mysid abundances, but negatively correlated with hydrobid snail abundances, irrespective of salinity. Gammarus amphipod abundances were positively associated with hypoxia duration when accounting for ocean-influence, and abundances were highest with intermediary hypoxia among mid-estuaries. These investigations highlight that local hypoxic conditions are the most direct feature affecting mobile invertebrate assembly within shallow estuaries.